Acute lung injury is a common disorder with no known, effective, pharmacologic treatment. One of the central contributing factors to the development of acute lung injury is an increase in the permeability of the pulmonary vasculature. Mice homozygous for a null mutation in the integrin (35 subunit gene, generated in the principal investigator's laboratory, are protected from pulmonary edema in a model of ventilator induced lung injury, and a blocking monoclonal antibody against the av(35 integrin protects wild type mice in this same model and also protects rats from pulmonary edema induced by unilateral lung ischemia and reperfusion. Blockade or genetic ablation of the av(35 integrin protects cultured endothelial cells from increases in monolayer permeability and from both the formation of rhoA-induced actin stress fibers and the phosphorylation of components of the endothelial adherens junction. In the current proposal, we will explore the molecular pathways linking the av(35 integrin to regulated increases in vascular permeability in more detail. We will use dominant negative and constitutively active constructs, siRNA knockdown and endothelial cells from knockout mice to test the hypotheses that this integrin regulates vascular permeability through interaction with the small GTPases, Ga12 and Ga13 and the known G protein activator integrin associated protein (IAP). We will then examine the in vivo roles for each of these proteins by studying ventilator-induced lung injury in mice expressing global or conditional knockouts of each of these proteins. Because our preliminary data suggest that av(35 is a central component of a multi-protein complex that contains Ga13, and many of the components of the rhoA dependent signaling pathway, we will examine which components of this complex depend on av(35 for assembly and which regions of the (35 subunit are required by reconstituting endothelial cells from (35 knockout mice with wild type, truncated and chimeric forms of this integrin. Finally, to determine whether the pathways we are studying are broadly relevant to non-cardiogenic pulmonary edema, we will further examine the role of av(35 and any other component found to be critical in three additional in vivo models - intracheal bleomycin, intratracheal endotoxin and the combination of low dose endotoxin and moderate volume ventilation. Through the proposed studies we hope to determine whether avp5 or other components of this pathway are attractive targets for intervention in acute lung injury.